The present invention relates to an improved manhole shield which is adapted to be supported on a manhole frame when the manhole cover is removed and act as a barrier to prevent water, dirt, tools and other materials from flowing or falling into the open manhole.
It has been known in the past to position shields around open manholes. When a manhole cover for a manhole that opens into an underground passageway, or an underground service chamber for servicing or repairing electrical, gas or water conduits and the like is removed, it is customary to position a shield or barrier around the frame opening to prevent tools, surface water and foreign material from falling into the opening and onto the workmen below the opening. It is also important to protect the utility conduits, switches, wires and instruments which may be exposed by the open manhole from the surface elements. Serious discomfort (and possible injury) to the workmen and serious damage to the facilities can occur if water or debris are allowed to enter the open manhole.
Manholes typically comprise circular access openings defined by heavy metal rings fastened to the top of standpipes. The rings are mounted flush with the surrounding road or ground surface and are relatively permanently attached to the adjoining street, roadway or other surface covering. In general, an annular recessed groove is provided around the inside top surface of the ring and a heavy metal lid (a/k/a "manhole cover") is positioned in the groove covering the opening.
In the past, shields or barriers were made generally corresponding to the diameter of the opening and were positioned around the opening or in the manhole cover recessed groove. Initially, these devices were caulked or packed in some manner in an attempt to prevent water from entering the opening. Not only was this time consuming and expensive, but often the caulking or packing did not seal the opening sufficiently. Other problems related to the fact that the frame rings often had significant dimensional variations and many were provided in different sizes. Rings which varied widely in diameter and which were not truly circular in shape were difficult to seal.
Some attempts have been made to solve some of these problems and provide better and more versatile open manhole shields or barriers. These are shown, for example, in U.S. Pat. Nos. 3,294,000 and 4,029,425 which disclose the use of a one-piece shield which relies on an inflatable gasket to seal the opening in the cover recess. The shields shown in these patents still are limited in their ability to seal openings of varied diameters, to provide positive seals, and to create stable shields.
It is thus the main object of the present invention to provide a manhole opening shield which is an improvement over known shields.
It is another object to provide a manhole shield which provides a more positive seal, is able to be used in more openings of varied diameters, and is stable once it is set in position than known shields.
It is a still further object of the invention to provide a shield which is light in weight, durable, convenient and easy to use, and which stacks for storage and/or to provide a higher shield when necessary.
These and other objects will be apparent from the following drawings and description of the invention.